An analog-to-digital converter (ADC) is employed to change/convert an analog input signal into a digital output signal. There are several different types of ADCs in current use, including pipeline, flash, and folding. For pipeline ADCs, separate decoding stages are arranged in a pipeline to convert the analog signal into a digital signal.
In a flash ADC, k bits of resolution employ 2k comparators to convert an analog signal into a digital signal. Folding ADCs are a variation of a typical flash ADC architecture except that they are arranged to map the analog input signal range into N regions where each of these N regions share the same comparators. In a folding ADC, the total number of comparators is typically 2k/N. Also, a folding ADC includes a coarse channel for determining from which of the N input regions the analog input signal originated. Usually, the coarse channel is configured to use coarse reference voltages that are spaced according to the voltage spacing between each folded region.
An ADC may employ a sample-and-hold circuit to relax the timing requirements of the ADC.